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Up next, a Niagara Falls of the Arctic, lakes of melted snow and ice in Greenland that are there one day, gone the next, draining so fast through cracks in glaciers that a big swimming pool would empty in seconds and an entire lake drains in a matter of hours. Joining us now are the scientists who have the job of sticking their heads into these giant fissures and figuring out where all those water is going and how it makes its way thundering through the thousands of feet of ice out to sea. Scientists trying to predict sea level rise due to global warming are interested in answering that question as they want to know whether all of this water may lubricate the second largest ice sheet in the world, help it slip into the ocean and dramatically raise sea levels around the world.

Joining us now to talk about their research out in today's issue of the journal, Science, and to talk about the hazards of working on the ice, picture an inflatable boat in the middle of a lake on top of a huge slab of ice that may drain itself out at any minute and you don't know about it, are my guests. Sarah Das is a glaciologist at the Woods Hole Oceanographic Institute in Woods Hole, Massachusetts. She joins us from member station WCAI on Cape Cod. Welcome to the program, Dr. Das.

Dr. SARAH DAS (Glaciologist, Woods Hole Oceanographic Institute): Thank you very much. It's great to be here.

FLATOW: You're welcome. Ian Joughin is a glaciologist in the Polar Science Center at the University of Washington in Seattle. He joins us from KUOW in Seattle. Welcome to the program, Dr. Joughin.

Dr. IAN JOUGHIN (Glaciologist, University of Washington, Seattle): Thank you and I'm glad to be here.

FLATOW: Thank you for both of us. It would seem - is this about an issue, Dr. Joughin, about - of ocean - trying to figure out how fast the oceans would rise if we lose the Greenland Ice Sheet and the mechanism for that happening?

Dr. JOUGHIN: Exactly, essentially an ice sheet collects a lot of snow each winter that - then glacial flow carries toward the ocean, much like rivers carry water from the other continents. And at the edge of the ice sheet, that ice either melts off in the summer or it gets discharged to the ocean as large icebergs, such as the one that sunk the Titanic. It came from Greenland. Right now, it's about 50/50, about half the amount of snow that's lost each year is through melt and about half from these outlet glaciers carrying the ice rapidly toward the sea. So what our study looks at is how fast the melt on the surface of the ice sheet can lubricate it and how, if that can speed up the ice and quicken the pace at which it's putting ice into the ocean. Of course, in a warming climate, you'd expect the ice sheet to discharge more ice than snow that falls each winter and the ice sheet would shrink and the sea level would go up. And then conversely, in an ice age, you'd expect the ice sheet to grow at the expense of the ocean which would drop.

FLATOW: So, Dr. Das, is the question then weather(ph) - I mean, because this is what we were assuming. We were assuming that all of this water rushing through the cracks and fissures, and I say we - the scientists would talk - they'll tell us, would lubricate, right? With - or make that giant ice sheet slip and fall into the ocean fast. Ease its transition?

Dr. DAS: That's right. But that's only been the sort of thinking for the last six years or so. There was a landmark study published in Science in 2002 that showed that portions of the Greenland ice sheet were speeding up during the summer time in an area that we didn't expect to be sensitive to seasonal change or to surface meltwater. And this led to a lot of new research, which included the work that we're doing, to try to understand why the ice might be going faster in the summer, and if it was going faster in the summer in many places, that would mean that the ice flow itself was sensitive to variations in climate. And that's because the ice is flowing over the bedrock underneath...

FLATOW: Right.

Dr. DAS: And where it has meltwater underneath, that acts as a lubricating layer, allowing the ice itself to flow faster.

FLATOW: Dr. Joughin, the paper showed that it did not seem to be speeding up this process. Would that be correct?

Dr. JOUGHIN: What it essentially showed was that everywhere on the ice sheet was speeding up by about 50 to 100 meters a year in the summer, and - or everywhere where there was surface melt. And part of the ice sheet is moving fairly slowly at about 50 to 100 meters a year. So there it's actually about a 100 percent speed-up. But the cause for real concern is these outlet glaciers that are discharging these icebergs to the ocean, and they're flowing much faster at one to even 10 kilometers a year. And in that case, the 50- to 100-meter year speed-up is relatively small. Some of what happened in the past was people had observations that were expressed as a percentage. So we were seeing the ice sheets speeding up by 30 percent, and that was being extrapolated to outlet glaciers and what we see is it's not so much a percentage speed-up, but just everything speeds up by the same amount, which is relatively small on the fast-moving glaciers where we're really concerned.

FLATOW: 1-800-989-8255 is our number. You can also go to Second Life, have an avatar, you can ask a question here. Let's set up the situation here on Greenland, because it's a fascinating scientific bed of research, and scientists go to certain places all the time over and over again, because they have information that they want to continually confirm or look at. And let's talk about these lakes that form. These lakes, we mentioned that they come from the melted snow and ice that form in the winter, and then they melt in the summertime. Are you saying that scientists get in a boat, and they go out into these lakes? Were you both in a little inflatable boat on a sleigh?

Dr. JOUGHIN: Just I was on the boat. Sarah was home having a baby that summer. So...

FLATOW: Well, that's important, too.

Dr. JOUGHIN: She sent me to go and do the dangerous stuff.

FLATOW: We don't want you on a boat in that condition.

Dr. DAS: I sent my people out to do that.

FLATOW: So, you're floating on this boat in a lake. How big is the lake?

Dr. JOUGHIN: It's about two miles wide. When you're in the middle it feels like you're out in the middle of there.

FLATOW: It's two miles wide, what, 40, 50 feet deep?

Dr. JOUGHIN: Yeah, about 40 feet deep and actually, there's some big holes in the middle that are may be - our sonar was suggesting we're 80 feet deep. So, it was a little intimidating sort of having the boat circle over those holes as we tried to map them.

FLATOW: And you discover, and in this paper, you talk about the ability of fissure to crack open in the middle of this lake and drain it at the rate of Niagara Falls.

Dr. DAS: That's right.

FLATOW: Sarah.

Dr. DAS: What we found with our instruments that we - after the team left the site in 2006, about 10 days or so after they were out floating around on that little lake. This entire lake, which was over three kilometers wide, did drain very rapidly through a crack that ran across the bottom of the lake. And it turns out that the lake drained its entire volume so over 11 and a half billion gallons of water in about an hour and a half. And our instruments that were left both on the lake floor itself - so pressure loggers that would tell you changes in water level, the height of the water through time, as well as instruments that were on the shore of the lake, including GPS sensors and seismometers gave us a really nice view - a very detailed view of how quickly the water disappeared, as well as the ice sheet response.

FLATOW: This is Talk of the Nation's Science Friday from NPR News. And so, you have this fissure and that it - that from what I understand is as big as the Horseshoe Falls itself if you would straighten it out, right?

Dr. DAS: That's right. It's about the same length.

FLATOW: Yeah, it could be that big and the same amount of water that would be...

Dr. DAS: It's actually quite a bit more water, yeah. We like to use the Niagara Falls analogy because that - that gives people something to visualize.

FLATOW: Right.

Dr. DAS: And it turns out that our maximum discharge of water through that crack was close to 9,000 cubic meters a second. And Niagara Falls, the - I was trying to look up the average flow, used to be around 6000 cubic meters a second. So, it was about one and a half times that flow. Right now, if you go to look at Niagara Falls though, there's actually quite a lot less water going over because a lot is diverted for hydropower, electric use. So, it's more like triple the flow of Niagara Falls.

FLATOW: So, Ian, you're out in this boat, in this lake, 10 days before, you - it could have opened right under you, could it have not?

Dr. JOUGHIN: Fortunately, it did not. For obvious reasons, we're done doing boating on lakes in Greenland.

FLATOW: For obvious reasons.

Dr. JOUGHIN: From now on, we'll just go out when the - after the lakes have drained where we can safely walk out there and just place the instruments on the surface, rather than trying to deploy them from a boat.

FLATOW: Now, we have pictures on our Web site, it's sciencefriday.com, of the size of these cracks. And I think we have a picture of you, Sarah, looking over, or placing these instruments, right?

Dr. DAS: Right.

FLATOW: By this crack.

Dr. DAS: Right. Yeah. The surface of an ice sheet, I think, people envision it sometimes as sort of a flat, white, featureless kind of surface. But in the summer melt season, an ice sheet is really a very dynamic, and interesting place and the surface is covered with little pools of water that you might stick your foot in inadvertently, streams of melt water rushing by, little hills and hummocks, depressions, which is - where the lakes fill in these cracks. And it appears from pictures that it would be a quite a slippery environment with all this water and ice, and anyone is used to walking around outside, you know, in a winter day when there's some water, might think that. But in fact, the surface is quite rough. So, it - you know, you're standing near a crack, but you're not really in any danger of falling in it.

FLATOW: Yeah. We - it - you can see the picture on our Web site. It does this very irregular surface.

Dr. DAS: That's right.

FLATOW: But then again, the - you have all this - you have this crack that's what, 3,000 - it could be 3,000-feet deep down to the bedrock.

Dr. DAS: That's right. The lakes that we were - the lake in particular that we focused our study on, the ice thickness there was close to a kilometer thick, so over half a mile of ice thickness.

FLATOW: So, you're looking into the abyss, down...

Dr. DAS: That's right.

FLATOW: What does it feel like?

Dr. DAS: Oh. It's a very dramatic feeling. Some of the areas where we were walking around there were still big streams that were flowing into these cracks and you'd see the water just disappear straight down into darkness, and you couldn't see very far down in them. But the most dramatic feeling was that you'd be standing there and the whole ice surface would be sort of vibrating, and thundering under your feet. And it just felt like the whole thing was, you know, was responding to this giant waterfall.

FLATOW: Somewhere else, there's a Niagara Falls going on under there.

Dr. DAS: That's right.

FLATOW: And you can feel it.

Dr. DAS: Yeah. You can really feel it.

FLATOW: All right. We're going to take this as an exciting story. We're going to talk more about it, take a break, our number, 1-800-989-8255. Talking with Sarah Das of Woods Hole, and Ian Joughin of the Polar Science Center, University of Washington in Seattle. Stay with us, we'll be right back. Take it back to Greenland, and put your pitons on, we'll be doing a little more walking out on the ice. Stay with us.

(Soundbite of music)

FLATOW: You're listening to Talk of the Nation, Science Friday. I'm Ira Flatow, a brief program note. This coming Wednesday, Neal Conan, broadcasting live from the new museum in Washington and if you're going to be in Washington, and you want tickets to join, as they say, the live audience for a live broadcast of Talk of the Nation, send an email to talk@npr,org, and make sure you put the word "tickets" in the subject line, or else the Spam filter will eat it up, we'll never see it again, now "tickets" in the subject line. We're talking this hour about the glaciers in Greenland with my guests, Ian Joughin, glaciologist in the Polar Science Center at the University of Washington in Seattle. Sarah Das, glaciologist at Woods Hole Oceanographic Institute in Woods Hole, Massachusetts. Our number, 1-800-989-8255. And when we last left, I talked about pitons, I should have said crampons. Do you wear crampons on the ice out there, or are you just wearing your sneakers?

Dr. JOUGHIN: We actually can walk around just with boots.

FLATOW: It's not that much ice climbing going on around there.

Dr. JOUGHIN: No.

FLATOW: When I last left you, Sarah, you were talking about looking in to the crevasse. Are you able to track, actually, the root of all that water, and we're talking about more than Niagara Falls going out to sea? Can you see it come out the bottom, so to speak?

Dr. DAS: We haven't been able to observe it coming out so far. One of the ideas we have for some future work, is to try to actually trace the water flow once the cracks have opened up. So, we're trying to design an experiment where we might be able to put some sort of benign tracer in at ice sheets...

FLATOW: Like a dye or something like that?

Dr. DAS: A dye or something like that, and try to detect it when it surfaces. The lake we're studying is about - there is about 40 kilometers underneath the ice before it reaches the ocean.

FLATOW: Ancient technology. I would think that there's got to be a little radio transmitting capsule that you could see.

Dr. DAS: People are working on that. Stay tuned.

FLATOW: That would give you the depth. The location has got a - you know, a global positioning thing in it that'll tell you exactly to the inch where it is.

Dr. DAS: There's actually something very similar to that being designed in Bristol right now. It's called the Cryo-Egg, so.

FLATOW: And you know, it would get stuck somewhere, of course, because that's what happens when you don't want it - to get stuck.

Dr. DAS: Well, maybe it will be smart enough to melt itself out.

FLATOW: Ooh, a little heat unit in there. Wow, we're designing it on the fly here. What the spec should be, it melts itself out, it gets a little rudder on it to stay in the water, and then an antenna pops out.

Dr. DAS: There you go. And if it could serve espresso with it.

FLATOW: How long do you have to stay out there at any one time to do this? You set up a base camp? Or are you out in tents? How does this work?

Dr. DAS: We go out by helicopter and we set up a camp. We have two lakes that we actually have study sites at. So, we'll camp at each lake for a week or so at a time. And we'll set up our tents. We have - and we each have our own tent that we sleep in - and we have a big cook tent where we prepare our meals, and store our food, and look at our data in the evening.

FLATOW: So, what do we then know about where the water goes? If anything?

Dr. DAS: What we can tell so far from our instrument observations, is that the ice sheet surface is responding at the same time that the water level is dropping in the lake. And what that tells us very clearly, is that because the ice around the lake rises up and is displaced at the same time that the water is lost from the surface, that it's reaching the base and then actually forms a temporary subglacial lake, so sort of like a blister underneath the ice sheet. And then over the next 24 hours or so, after that blister has been injected, so to speak, under the ice, it drains away in it. That water flows in to some sort of subglacial hydrologic system, either a pre-existing system, or it's forming its own drainage system.

FLATOW: Let's go on to the phones. Ryan in Greenville, Missouri. Hi, Ryan.

RYAN (Caller): Hi. How are you doing?

FLATOW: Hi there.

RYAN: Good. I'm in Greenville, Michigan by the way.

FLATOW: Oh, Michigan. Sorry.

RYAN: My question was, I wasn't sure how wide these cracks were, and if the scientists were actually able to lower themselves inside. And if they were, if they were - had any knowledge of any caverns - any ice caverns underneath?

FLATOW: Yeah. Do you - there...

RYAN: I guess, what I'm thinking more like, you know, Aladdin under not the sand obviously, but with ice.

Dr. DAS: There are ice climbers and mountaineers out there that have been exploring features like this both in Greenland and in other glaciers. People tend to wait until the water flow has stopped at the end of the summer to go down so they're not washed away. This is not something that we chose to do.

RYAN: Great. Well, thank you very much. I appreciate it.

FLATOW: You're welcome. And you're not going boating anymore?

Dr. DAS: No.

FLATOW: Ian, you're looking at whether the meltwater that Sarah is talking about is enough to speed up the flow of the ice sheet into the ocean, correct?

Dr. JOUGHIN: Yes. Yes. And that was a concern in the recent IPCC, the Intergovernmental Panel on Climate Change. It's interesting we're talking about hurricanes on - in the last segment and how the models don't really capture hurricanes in that scale. And that's a problem with ice sheets too. Many of these fast-flowing glaciers are only about five kilometers wide and typical model resolution might be something more like 20 kilometers wide. So, they're not really capturing a lot of these fast effects. So, the recent IPCC, using sort of models like that. made fairly conservative predictions, and then there was a big concern that there were lots of things going on. Many of Greenland's large glaciers have doubled their speed over the last five or 10 years as temperatures have warmed in Greenland.

And one of the concerns again was whether this meltwater was what having the effect and lubricating the ice and causing those speed ups. And essentially what our work shows is that, it's probably not the direct lubrication from meltwater that's causing the big changes. Nonetheless, these big changes are occurring. It's not - so essentially we've ruled out one sort of potential hypothesis for what's going on. But we're certainly not out of the woods yet as there are really large changes happening in Greenland right now.

FLATOW: You have any ideas or thoughts, theories, your own pet theory?

Dr. JOUGHIN: Well, one way to think of it, a glacier is, or an outlet glacier is, is like a tube of toothpaste, the ice sheet and the fjord is like the nozzle coming out of the, the flows coming out into the ocean. And like my kids occasionally leave the top off the toothpaste and it all gets kind of gunked up and then they come and squeeze on it eventually that little plug comes out. And essentially, that's what's happening in the fjords. The ice in the narrow constricting fjords is retreating and calving back as temperatures warm, and it's sort of like removing that plug of toothpaste, allowing the toothpaste or the ice to squeeze out more rapidly behind and flood into the ocean. And so, it's likely some kind of effect like this though it's not a simple relation to climate. We don't exactly understand why the ice retreated in the first place.

FLATOW: We have seen similar sorts of worries and actions going on in Antarctica with some of these big icebergs calving off. And the breaking away of a lot of ice from - they might be blocking the, you know, keeping the glaciers on the shore from sliding into the ocean.

Dr. JOUGHIN: Exactly. There are floating ice shelves in Antarctica that are sort of serving the same purpose that this ice in the fjords is serving to hold back the inland ice. And when those ice shelves break up, it just happened on the Larsen B, the glaciers behind them can start flowing to the ocean much more rapidly. I believe on - some of these glaciers are flowing eight times the speed they were originally.

FLATOW: Let me ask both of you, when you - do you ever feel the ice just move when you're standing on it?

Dr. JOUGHIN: No.

FLATOW: Does is take a little jump that - how far - how fast is the - does the glacier move in a day or a week or a month when you're there?

Dr. DAS: The area...

Dr. JOUGHIN: Where we are...

Dr. DAS: Yeah. Go ahead.

Dr. JOUGHIN: Where we are, it's moving about a foot a day. And on the faster moving areas on the outlet glaciers it could be moving a hundred feet a day.

FLATOW: Wow.

Dr. DAS: So, we didn't feel the motion but one of the things that we would not really feel but hear is every so often you'd be in your tent sleeping, and it would be quiet, and you will just hear a loud pop or a snap and you'd think, you know, was that a lake draining, was that a big crevasse opening up somewhere. And you'd look out and everyone is poking their head out of their tent. You know, looking around, trying to see where that came from.

FLATOW: Wow. Did you ever listen? I mean, when I was in Antarctica I brought my microphone. I would stick it on to the ice and hear the glacier melting.

DR. DAS: Yeah, you could hear that, and you could hear the water sloshing around in the lake.

FLATOW: Yeah, I'm thinking you know, it's solid and sound travels a long way, maybe you could hear the Niagara Falls by just, you know, listening with some instruments on the ice, something like that.

Dr. DAS: Right. In fact our seismometers did detect quite a lot of that sort of waterfall sound, so to speak. We expect that our seismometers will be mostly sensitive to the fracturing of the ice when the crack was opening up, but it seems to be equally sensitive to the energy from the rushing of the water down through the crack both hitting the walls of the ice as well as probably pounding into the bedrock below.

FLATOW: 1-800-989-8255. Sheila in Boston. Hi, welcome.

SHEILA (Caller): Turn on the radio.

FLATOW: Yeah, you got to turn the radio on and then turn it off.

SHEILA: Hello.

FLATOW: Hi, there.

SHEILA: Hi, how are you? Wooh! Are you still there?

FLATOW: I hope you're still there and you're OK.

SHEILA: Yeah, did that hurt? I hope your head is OK. I dropped the phone on the floor. I have a question that may not actually be appropriate for this show about glaciers. But in terms of you know, the ice caps melting, the glaciers melting, and so forth, I see documentaries, and they have these big icebreaker ships that go right in and they measure, they take all these observations and so forth. Wouldn't the act of taking the icebreakers in and breaking the ice, what is it - they cause more surface area on the edge of the ice - doesn't that very fact increase the melting rate?

FLATOW: Ian, are you going to take a stab at that?

Dr. JOUGHIN: Yeah, there you're talking about sea ice rather than glacial ice. So, in Greenland we're talking about several 100 meters thick of ice that's formed from snowfall. What you're talking about is the floating ice that freezes directly on the surface of the ocean in the Arctic. And I suppose, you could have a little bit more of local melting from the icebreaker, but when you consider how small that icebreaker track is relative to the whole Arctic Ocean, I would think it would be fairly minimal.

FLATOW: Have you noticed the change in the sea ice, since you've been going there? Oh, you know, the Arctic sea ice.

Dr. JOUGHIN: That's essentially what everyone else in my center works on. I work mostly on the glacier ice. We do think the sea ice may be having an effect on the glaciers on how fast they calve icebergs and suppress the calving of icebergs in the winter, which may have something to do with this retreat, certainly in Disco Bay where this large outlet glacier, Jakobshavn, calves into, the time that its ice shelf and it broke up, and started speeding up, was also a time of quite low sea ice in the winter.

FLATOW: Just give us an idea of how much ice is locked up in Antarctica, in Greenland compared to Antarctica.

Dr. JOUGHIN: In Greenland, we're talking about sort of five to seven meters of sea level rise, so about 20 feet of sea level rise if the whole ice sheet went away. And we're talking about by 10 times that much if all of Antarctica went away, though much of Antarctica is considered relatively stable. The west Antarctic ice sheet, which is the smaller part of Antarctica, is believed to be somewhat unstable, and that could likely contribute about 20 feet of sea level rise too, if it were all to go, like it has probably during past periods between ice ages.

FLATOW: Lets go to Vinch(ph) in Sacramento, hi.

VINCH (Caller): Hi, you know, I'm still trying to rap my head around how quickly that lake drained. That was amazing. And I've just - I've got to know, if you were in your boat when that lake, that plug went in that lake, could you have gotten off the lake alive?

Dr. JOUGHIN: I wouldn't want to try it. I don't think the odds would have been good.

Dr. DAS: Yeah. I don't think so.

VINCH: I mean, the force of the water as it funneled into that hole must have been dramatic. And so...

Dr. DAS: I mean...

VINCH: I don't know, it...

Dr. DAS: One...

VINCH: It would have been something to see, I guess.

Dr. DAS: One possibility, that lake actually - the lake level started to drop for about 16 hours or so before the rapid drainage. It was va ery, very slow drop but you know, it's possible that there was some activity in the ice that you would hopefully have detected or some sort of warning sign, you know, if you were going to do this again, I suppose you could try to set up a warning system that would alert you that it's about to go. But it's very hard to predict when these things actually drain.

FLATOW: This is Talk of the Nation Science Friday from NPR News. So, there must be lakes like this all over Greenland.

Dr. DAS: That's right. There're over a thousand of these lakes just on the western margin of the ice sheet itself that have been detected by satellites.

FLATOW: And do you keep going back to the same spot here to study what's going on or...

Dr. DAS: So far, we have two study spots and this coming summer will be our third year going back. We keep our instruments there year round. They're set up on towers on shore. So, we need to go back and download our data and reset the instruments for the following year.

FLATOW: Are there people...

Dr. DAS: And in the...

FLATOW: I'm sorry.

Dr. DAS: Future - sorry - in the future, we hope to study a few more locations as well.

FLATOW: Are there people there now?

Dr. DAS: No.

FLATOW: Work is done?

Dr. DAS: That's right.

Dr. JOUGHIN: The instruments are sitting there quietly recording data, and we'll pick them up this summer.

FLATOW: With - could there be a satellite photo of the lake shrinking in size some place?

Dr. JOUGHIN: We have images every day when there are cloud-free days, and they do show the lakes could drain overnight. We just didn't expect them to drain in 90 minutes.

FLATOW: Wow. Just trying to imagine that. And so you basically dodged the bullet on this one.

Dr. JOUGHIN: Very much so.

FLATOW: Interesting. Taken together, do you think that these studies mean that we shouldn't be concerned about the melting of the Greenland ice sheet? That we...

Dr. DAS: I think that's probably a little too strong of a conclusion to draw. I think that together they show us that we understand one more process in ice sheet dynamics a little bit better, and that's going to help our models constrain the future response of Greenland to global warming a little bit better.

FLATOW: Mm hmm.

Dr. DAS: But we know that Greenland is losing more mass, more volume of water every year than it's gaining, and it's contributing to the sea level rise today and it's certainly going to continue to do that into the future and so, whether, you know, we're going to have twice as much as we expected or not, I think we still have to be concerned because the current rate of sea level rise is not really something that our - that our countries internationally are prepared to handle.

Dr. JOUGHIN: That's the one thing that you know, you say to people, what are you doing? And they don't realize that this is going to happen no matter what to anybody.

Dr. DAS: I think there's a lot of people in a lot of governments with their heads in the sand about this issue.

FLATOW: Ian, what's your take on it?

Dr. JOUGHIN: I agree with Sarah. I mean, essentially the IPCC had a whole list of things that we really didn't understand and we've been able - we're starting to get a feel for how this one particular mechanism affects the ice sheets. But there're several more that we need to figure out and try and understand why there are large changes occurring now.

FLATOW: Could there - you're saying that they - in your study, you're not finding that the meltwater here is lubricating but you're finding the ice is moving very quickly. Could there be...

Dr. DAS: Well it - I mean, just to correct...

FLATOW: Yes.

Dr. DAS: It is lubricating the ice. It's just not lubricating to the extent that could explain these rapid changes in outlet glacier discharge that have been observed.

FLATOW: Could there be effects, you know, holding? You said it's - could be like a tube of toothpaste so there might be some effects on the shoreline that might be keeping it back, and then it suddenly pops out and moves down? Is that what you're thinking, Ian?

Dr. JOUGHIN: Well, this is the - down in the fjords, further down where there's a lot of retreat, certainly big sections of some glaciers have retreated back several kilometers over a single summer. And that's usually led to a big speed-up of the glacier behind it in discharging a lot more ice to the ocean. And so, it's that process that causes a glacier, that might have had a stable calving front in its fjord, where it calves off icebergs for tens of years at the time, why one summer all of a sudden, it happens to retreat back an additional say four or five kilometers? That's the kind of thing we're trying to understand right now.

FLATOW: Another great science mystery we love talking about. And I thank you for coming and talking about it with us. Ian Joughin is a glaciologist in the Polar Science Center at the University of Washington in Seattle. Sarah Das is glaciologist at the Woods Hole Oceanographic Institute in Woods Hole, Massachusetts. Good luck to you out there in Greenland.

Dr. DAS: Thank you very much.

Dr. JOUGHIN: Thank you.

FLATOW: And if you have anything new, come right back on and we'll talk about it some more.

Dr. DAS: Would be glad to.

(Soundbite of music)

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